D. Coping with the Sun on Mount Everest
Mount Everest is an environment of extremes in all weather conditions, but
this is especially evident in temperature and UV (ultraviolet) exposure.
Both temperature and UV problems on Mount Everest are a function of the
physical environment (especially snow) and the high altitude. Temperatures
can reach as high as 41 degrees Celsius as the sun's rays pierce the thin
atmosphere found at this elevation and are reflected by the snow.

As a result of the high altitude, temperatures can also get as low as
minus 46 degrees Celsius on the upper parts of the mountain (the
troposphere decreases in temperature with height), but the sun's rays are
even more of a danger at this altitude despite the cold.

WHY?
At sea level and elevations much lower than that of Mount Everest, only 47
per cent of the energy from the sun hits the ground. The atmosphere
absorbs the other 53 per cent or it gets reflected back into space. Then
the heat is distributed through the air by convection. Note: The amount of
heat in a region of the earth is determined by its proximity to or from
the equator (see Section A, Climate and Weather).

Since Mount Everest is 8,050 metres (29,035 feet) high, it is in the
uppermost part of the troposphere layer of the atmosphere that helps to
protect the Earth from the sun's UV rays.

This means that a large percentage of the harmful rays that are
filtered out gradually through the atmosphere at lower altitudes (where
most people live) are not filtered on Everest. Climbers at this height are
exposed to very dangerous levels of ultraviolet radiation.

Also, 85 per cent of UV rays that do reach Earth (of which most are
absorbed at lower altitudes) are reflected off the fresh, white snow,
almost doubling the radiation exposure in this environment (Canadian
Dermatology Association, Sun Facts).

The sun's UV rays have the potential to be extremely dangerous for high
altitude climbers, as well as for those people who live at relatively high
altitudes on a year-round basis such as the Sheraps in the Mount Everest
area of Nepal. Even more alarming is how little exposure is required to
cause serious damage in a very short time.

New research from the American Academy of Dermatology (AAD) can be
interpreted to show that UVB levels are 29 times more intense at the
summit of Mount Everest than they are at sea level. This means that a
climber with an average complexion (neither extremely light nor dark)
would develop serious sunburn in less than six minutes. In fact, the
research says that the same person would sunburn after six minutes at only
11,000 feet (3,353 metres) compared to 25 minutes at sea level. These
numbers are based on a clear day at noon in either location, with no UV
protection such as sun block or protective clothing.

With this kind of information, it is easy to see why climbers have to
protect their skin from the sun's rays and the glare from the snow, which
increases the intensity of the UV rays. This is just as important as
protecting themselves from the extreme cold to avoid serious skin damage.
With the sun there is the added danger of increasing your chance of
developing skin cancer (Melanoma).

People who live in higher altitudes and in areas where the ozone layer
is thinning need to be educated by their local health organizations and
governments to protect themselves from the sun more carefully. There is a
major education program being conducted by the government of Australia,
since its population of citizens has had dramatic increases in rates of
skin cancer in recent history.

This is due to a large number of fair complexions in an area that has
the highest levels of solar radiation on earth.

Also, human pollutants to the environment are damaging the ozone layer.
There are places in the ozone layer that are either disappearing or
thinning at an alarming rate, which is leading to compounding rates of
skin cancer as a result of more UV rays (particularly more UVB) passing
through the atmosphere to Earth. People burn faster than they did before
with the same amount of sun exposure time.

Protect children by keeping them from excessive sun during the hours
of strongest sunlight, by applying sunscreen liberally, and frequently
to children older than six months of age.

What is the difference between UVA and UVB radiation?
There are actually various types of radiation emitted from the sun,
including visible light and infrared radiation, but it is ultra violet
radiation that most affects our skin and eyes. In addition to UVA and UVB
rays there are UVC rays. UVC rays are stronger than UVA and B, but they
are filtered out by the ozone layer of the stratosphere and do not reach
the earth.

UVB (ultraviolet B) - is responsible for sun burns,
delayed tanning (the process continues in the skin after sun exposure is
ended), aging, cataracts of the eye, and genetic damage that can lead to
skin cancer. UVB rays are short wave radiation. They are the most powerful
and potentially harmful, even though much of UVB is filtered out by the
ozone layer in the stratosphere. The closer you live to the equator, or
the higher the elevation, the more intense exposure is received. Other
indicators for intensity of UVB exposure are time of day, season (winter
has less direct sunlight) and cloud cover (dense, dark cloud cover does
filter UV, though haze and light clouds do not).

UVA (ultraviolet A) - causes immediate tanning and
contributes to premature aging and possibly skin cancer. There are no
regulations for UVA protection in sun block creams and lotions. The one to
15 ratings (and higher) indicate the level of protection from UVB. UVA
rays pass through the ozone layer and until recently were considered to be
harmless. The current status of this information is due to relatively
recent studies. The waves of this radiation are longer than UVB and the
exposure is virtually the same all year.

Why does the sun affect our skin the way it does - with suntans and
sunburns?
First of all, we have to know something about our skin. Skin is one of the
body's organs - the largest one in fact. It has cells and tissues that
perform a specific function of protecting the body.

It is made up of two main layers (with other layers within them), the
outside layer being the epidermis and the inside layer being the dermis.
Skin has many sensors, which makes it sensitive to heat, cold, pressure,
itching and pain. Being sensitive is good for us because it warns us when
something is damaging our skin.

The part of the skin that we can see on the outside of our body is only
the first of many layers of our skin organ. In fact, all we see is the
layer of dead cells that make up the stratum corneum layer of the
epidermis (or the outside part of our skin).

The part of your skin that is responsible for the development of a
suntan (or burn) is the malpighian layer of the epidermis. The epidermis
has several layers within it. On the outside is the layer of dead skin
cells that we see called the stratum corneum - what we call our skin. Then
comes the malpighian layer, which contains the granular layer, the spinous
layer and the basal layer.

The basal layer of the epidermis is the last layer before the dermis
layer. The basal layer contains melanocyte cells that produce melanin -
the pigment that reacts to the sun to create a tan, and they are the cells
that are responsible for melanoma, a form of cancer associated with sun
exposure on the skin. All people have approximately the same number of
melanocytes; the difference in the color of our skin is determined by how
much melanin they produce.

What causes tans?
Upon exposure to sunlight, melanocytes increase in activity as a reaction
to the UV rays from the sun to produce tanning. They produce more melanin
pigment, which causes the darker appearance of the skin.

Actually very brief exposure to sun for Caucasians builds protective
melanin in your skin. Production of melanin takes quite a long time, but
the brief exposure to UV rays is enough to stimulate the melanocytes into
production of melanin which continues even after coming in from the sun.
If you expose yourself very briefly to the sun for five to seven days,
Caucasians can build pigment levels that are protective.

The same cautious approach is not as necessary for races with dark skin
since their skin produces melanin on a continuous basis, which provides
more protection from UV radiation of the sun. This information however is
only related to short exposure and as one of the ways to prevent burning.
Any exposure to the sun, especially during 11 am and 4 pm will contribute
to aging effects of the sun, particularly with prolonged exposure without
proper protection including appropriate clothing and sunscreen.

What causes burns?
We recognize sunburn as red, painful skin that can have blisters in very
extreme cases. It occurs after long term exposure to the sun without
proper protection (the actual damaging amount of time depends on your
natural skin pigmentation - whether it is light or dark). We often say,
"I didn't really realize I was getting burned until after I came
inside". This is because burns are caused by UVB rays which are
responsible for delayed tanning and sunburn in severe cases.

When you get a sunburn you are experiencing damage at the cellular
level. In reaction to this damage, the body increases blood flow to the
skin to help repair the damage. The increased blood flow is the source of
the redness and causes extra blood in the upper layers of your skin.

What causes melanoma or skin cancer?
Melanoma is caused by UV radiation damage to the melanocyte cells.
Repeated exposure and damage caused by UV radiation can cause cancerous
mutations of the cells.

The sun protection factor (SPF ratings) found on sunscreen and sun
block creams and lotions indicates the product's ability to block UVB
rays. Dermatologists advise that you choose a SPF factor of at least 15,
regardless of your skin type. If you are very fair, you should seek higher
SPF levels.

For protection from UVA in your sunscreen, look for the term
"broad spectrum protection". The product should also be approved
by your national dermatology association. You may also contact your
dermatology association for a list of approved sunscreens.

Ingredients to look for are:

Melanin - some producers are adding this to sunscreen, so that,
just like the body, it will absorb the UV light, therefore blocking the
skin from the UV.

PABA (para-aminobenzoic acid) - is being used less in products
now because of the high instances of allergic reactions. PABA filters UVB
light.

Titanium dioxide - blocks UVA and UVB. This is the type
recommended for sensitive skin and high altitude exposure as a complete
blocker of sunlight for the skin. A Calgary dermatologist has recommended
the team use brands which are chemical free, meaning that they do not have
a lot of other ingredients like moisturizers, etc. They are strictly used
for the purpose of blocking the ultraviolet rays.

Don't we need the sun's ultraviolet rays for vitamins?
Yes, humans do need Vitamin D to metabolize calcium. We can get that from
ultraviolet light, which converts 7-dehydrocholesterol in your bloodstream
into Vitamin D. However, we also have Vitamin D fortified milk and in the
past, we took cod liver oil. For more details, please see the "How
Vitamin D Works" section of How
sunburns and suntans work.